Reef Shark & Predatory Teleost Abundance and Assemblage Composition in the World’s Largest Shark Sanctuary

Authors

Naomi Frances Farabaugh, Florida International UniversityFollow

Document Type

Dissertation

Degree

Doctor of Philosophy (PhD)

Major/Program

Biology

First Advisor's Name

Michael Heithaus

First Advisor's Committee Title

Committee chair

Second Advisor's Name

Alastair Harborne

Second Advisor's Committee Title

committee member

Third Advisor's Name

Yannis Papastamatiou

Third Advisor's Committee Title

committee member

Fourth Advisor's Name

Joel Heinen

Fourth Advisor's Committee Title

committee member

Fifth Advisor's Name

Michelle Heupel

Fifth Advisor's Committee Title

committee member

Keywords

BRUVS, carrying capacity, biogeography, marine predator, marine conservation, shark sanctuary, boosted regression trees, marine protected areas, Elasmobranch, assemblage composition, species richness, Teleost Predators, Relative abundance, coral condition, coral health index CHI

Date of Defense

5-22-2023

Abstract

Populations of sharks and other marine predators have declined dramatically worldwide. Because sharks play a role in the dynamics of their ecosystems and there is increasing interest in rebuilding populations, understanding the factors influencing their abundances and assemblage structure are important for proper conservation management. French Polynesia is the world’s largest shark sanctuary and features gradients of environmental and anthropogenic factors; it therefore provides a model system for elucidating the factors that affect the abundance and assemblage compositions of elasmobranchs and large teleost predators. Using ~3000 hours of baited remote underwater video data collected across 17 islands and 35 reefs, I found that the relative abundances of sharks at high islands were only one third of that on atolls, and open atolls had abundances nearly 20% higher than closed atolls. Therefore, realistic conservation targets for reef sharks in the Indo-Pacific should account for island geomorphology. Other environmental factors had smaller effects and human pressures (market gravity) did not significantly influence abundances. Assemblages at most islands generally lacked rays and were dominated by blacktip reef sharks (Carcharninus melanopterus) and grey reef sharks (Carcharhinus amblyrhynchos). There was, however, significant variation in elasmobranch assemblages across French Polynesia. Species assemblages and associations, particularly at smaller scales, may be shaped by species interactions. Relative abundances of predatory teleosts from the families Lutjanidae, Scombridae, Megalopidae, Carangidae, Sphyraenidae, Serranidae, and Lethrinidae on 19 reefs across 11 different islands/atolls varied positively with net primary productivity. Island geomorphology, human population density, relative abundance of sharks, and sea surface temperature, also influenced predatory teleost abundances. Interestingly, higher abundances of teleosts were found on reefs with higher abundances of sharks. However, unlike sharks, predatory teleosts appear to be sensitive to fishing pressure at even low human population densities. Higher abundances of predatory teleosts and sharks, together, are generally positively associated with healthier reefs as measured by percent cover of hard corals and crustose coralline algae. The relationships between coral health, small teleosts, and both groups of predators, however, were non-linear and it is unclear if the presence of predators helps facilitate reef health or if healthier reefs attract greater abundances of predators.

Identifier

FIDC011107

ORCID

https://orcid.org/0000-0002-7839-7453

Recommended Citation

Farabaugh, Naomi Frances, "Reef Shark & Predatory Teleost Abundance and Assemblage Composition in the World’s Largest Shark Sanctuary" (2023). FIU Electronic Theses and Dissertations. 5337.
https://digitalcommons.fiu.edu/etd/5337